1. Field of the Invention
The invention relates to cameras and other optical devices in which variable fields of view are desired and are implemented in a compact and relatively inexpensive design.
2. Description of the Related Art
Optical devices having systems for varying the field of view are known in the art. Such devices are useful in, for example, infrared imaging and navigation systems where a very wide field of view might be required for one operation and a more limited, detailed field of view required for another.
Various methods are commonly deployed by conventional field of view varying systems. In U.S. Pat. No. 3,825,315 to Altman et al., a lens arrangement for infrared telescopes is provided with movable lenses which translate along the optical path of the system to continuously change system magnification and field of view.
In U.S. Pat. No. 3,947,084 to Noyes, a cam mechanism simultaneously translates one lens group linearly and another lens group nonlinearly along the system optical axis to achieve variable magnification and field of view. The system is designed for operation in the infrared wavelength range.
In U.S. Pat. No. 5,089,910 to Sigler, the lens elements of a catadioptric system are mounted for translation along the optical axis. The translation is also effected by a cam mechanism which imparts linear and nonlinear movement to the various elements involved.
In U.S. Pat. No. 5,151,820 to Sillitto et al., a pair of refractory elements are switched between two conjugate positions on the system optical axis to provide two distinct fields of view. The refractory elements, comprised of lenses, are mounted on a carriage which translates linearly along a track. A motor is provided for imparting motion to the carriage.
U.S. Pat. No. 5,229,880 to Spencer at al. shows a system in which one of two sets of optical elements is inserted into the optical axis to enhance the field of view of the system. Insertion of one set of optical elements provides an intermediate field of view, while insertion of the second set provides a wide field of view. The absence of either set from the optical axis retains the system narrow field of view.
U.S. Pat. No. 5,363,235 to Kiunke et al. shows a reflecting telescope arrangement which uses one set of optical elements to widen the field of view. When this set is disposed in the optical axis, the system achieves a wide field of view, while when the set of optical elements is retracted, a narrow field of view is attained. Motion of the optical elements is affected manually or electro-mechanically.
U.S. Pat. No. 5,024,493 to Fantozzi at al. shows a compact arrangement in which a specific combination of lenses and mirrors is used. The patent enables attainment of a long focal length in a relatively confined space, such as the turret of an aircraft. No provision is shown for varying the field of view of the device.